The following methods have been known as methods of forming polyimide patterns which use a composition of actinic radiation-sensitive polyimide precursors.
(A) A polyimide pattern forming process which uses a composition wherein carbon-carbon double bond which can be dimerized or polymerized by exposure to actinic radiation and wherein an amino group or a quaternary salt thereof are added to polyamic acid (disclosed, for example, in U.S. Pat. No. 4,243,743).
(B) A polyimide pattern forming process which uses a composition of polyamic acid with acrylamide added thereto (disclosed in, for example, EP Laid-open No. 430220) .
(C) A polyimide pattern forming process which uses a composition of actinic radiation-sensitive polyimide precursors wherein a photosensitive group is introduced to polyamic acid with ester group.
However, all of these processes are of negative type wherein the film in portions exposed to the radiation remains, because the irradiated pattern is developed in such a state that the film in the exposed portion has photo-cured to a greater degree than that of the unexposed portion. In negative type processes, dust on the mask used in exposure leads to a defect produced therein resulting in pin holes formed in the polyimide film. For this reason, there have been problems such as low yield of production and low reliability particularly where the polyimide coating is used as a protective layer for semiconductor elements or as an inter-layer insulation layer for multi-layer wiring in high-density packaging. Thus there has been a demand for a method of forming positive polyimide patterns by means of a composition of actinic radiation-sensitive polyimide precursors.
The following processes have been disclosed as methods of forming positive polyimide patterns by means of an actinic radiation-sensitive composition of polyimide precursors.
(D) Polyimide pattern forming processes which uses a composition of actinic radiation-sensitive polyimide precursors obtained by introducing a photo-degradable photosensitivity to polyamic acid with ester group (disclosed in, for example, Japanese Patent Laid-Open No.1-61747).
(E) Positive polyimide pattern forming processes wherein a naphthoquinonediazide compound of a particular molecular structure is added to polyamic acid having a particular structure and heat treatment within a particular temperature range is applied after exposure (disclosed, for example, in Polymer Preprints, Japan, vol.40, No.3, 821, (1991))
However, the processes described above have not been put into practice due to problems such as complicated process of preparing the composition of actinic radiation-sensitive polyimide precursors and lack of photosensitivity.
Accordingly, an object of the invention is to provide a process of forming an excellent positive polyimide pattern by using a composition of actinic radiation-sensitive polyimide precursors which can be easily manufactured.
Another object of the invention is to provide a process of forming a positive polyimide pattern having excellent photo-reactivity (photosensitivity, etc.).
Further another object of the invention is to prevent the yield of production and reliability from decreasing when the polyimide film is used as the protective layer for semiconductor elements or inter-layer insulation layer for multilayer wiring of high-density packaging substrate .